This invention relates to pneumatic tires and more particularly to a novel carcass structure specifically for use in aircraft tires.
An aircraft tire is subjected to extreme operating conditions which include very high internal pressure, high speeds in excess of 300 kilometers per hour, and very high deflections. During taxing and takeoff, the deflection may be more than 30%, and on landing 45% deflection or more occur under impact conditions. These extreme pressures, loads and deflections put the sidewall between the shoulder of the tire and the bead through severe tests. The high pressure and loads place the ply cords under severe tensile loads. The cords in the plies, particularly in the lower sidewall area, are frequently mechanically fatigued due to high heat buildup near the beads while the aircraft is taxing or during takeoff.
In the prior art, it has been conventional to increase the number of plies of the tire to increase rigidity and to decrease deformation under load. Also, much work has been directed to reinforcing the ply turnup portion of tires to improve durability.
U.S. Pat. No. 5,105,865 by Togashi et al, describes these conventional solutions and proposes that the durability of the tire can be improved by avoiding bending deformations of the ply surfaces. The patent describes a tire curvature that permits an increase in durability to be achieved with no increase in weight.
U.S. Pat. No. 4,029,137 by Robert Suydam teaches that an improvement in durability can be achieved by a novel wrapping of the ply structure about the beads. This invention also improves durability without increasing weight.
In British Patent GB 2 087 806 to Kaisha, a bias aircraft tire is disclosed wherein cords of the carcass plies are spaced further apart to achieve improved durability.
In addition to the normal loading conditions of aircraft tires, military aircraft, in particular naval airships, often are required to land on the decks of aircraft carriers. The landings are routinely harsh and rapid due to the shortened landing area. To stop the aircraft, an arrestor cable is employed. The nose wheel or main landing gear wheel of the aircraft impacts this 1-⅝ inch diameter arrestor cable on landings and can severely damage the tire. On the F/A-18E/F naval aircraft the main tire can see a camber angle of 10.2xc2x0. This means that one sidewall will take the initial impact at about five times the normal rated load. This pinches the impacted sidewall severely which can result in cut or damaged carcass plies. Repeated landings result in cumulative damage. To extend the life of the main tire additional full width carcass plies have been used; however, this imposes a weight penalty: A novel approach to improve sidewall durability while enabling a reduction in overall tire weight was disclosed in U.S. Pat. No. 5,637,764. In that patent sidewall cord reinforced inserts were used to replace full plies yet provide additional sidewall bruise resistance and increased durability of the tire carcass.
Advances in ply strength and the use of these inserts has resulted in sufficiently strong carcasses. The carcasses has become so strong that on the main landing gear of the F/A 18E/F naval fighter aircraft testing evidenced that the bead cores were being sufficiently stressed that the bead cores would fail prior to the crown reinforcement during burst test. This prior art tire is depicted in FIGS. 1 and 2. As illustrated the tire had originally 12 plies and three bead cores of equal size and construction. A more robust carcass construction was requested and it was discovered that the conventional three bead core design became a limiting factor wherein the beads would fail prior to the crown of the carcass during tire burst test. As a general rule, a tire engineer tries to design the tire such that tires fail in the crown area when subjected to burst testing.
It must be appreciated that the rim and the tire""s beads are confined to a limited amount of space. Accordingly, the simple addition of carcass plies means that the bead shape or configuration must be adjusted while still allowing for a proper fit to the rim. Ideally as tire designers improve the tires durability they strive hard to insure the rim design can remain unchanged. New rim designs are very costly and generally limit the use of improved tire designs to next generation vehicles or aircrafts.
It was an object of the present invention to design the tire to fit on the prior art rim while still improving the bead strength and the overall carcass strength.
It was a further object of the invention to design an aircraft tire having three bead cores in each bead portion with substantially much greater strength than conventional prior art tires they were to replace.
An improved bias aircraft tire has a carcass reinforced by six or more ply pairs the six or more ply pairs extend from one bead portion through a crown portion to an opposite bead portion. Each bead portion has three bead cores, a first heel bead core, a middle bead core and a third toe bead core. Each bead core has one or more ply pairs wrapped around and extending radially upwardly relative to the bead core.
The three bead cores in each bead portion are each of a substantially rectangular cross-section having a semi-rounded radially innermost portion. Each of the three bead cores have lateral rows and vertical columns of bead wires. Wherein, the middle bead core has at least one row or one column less of bead wires than the first heel bead core.
Each bead core has an inside diameter d. The middle bead core has a diameter dm less than the diameter dh, first heel bead core.
The toe bead core has one or more row or column than the middle bead core. The toe bead core has an inside diameter dT equal to or greater than the diameter dm of the middle bead core minus the differences in the diameter dH of the first bead heel less the diameter dM of the middle bead core or dtxe2x89xa7, dm, xe2x88x92(dhxe2x88x92dm).
In the preferred embodiment tire the pair of carcass plies equal 7. The heel bead core has 12 rows and 8 columns of wire totaling 96 wires when viewed in cross-section. The toe bead core is the same construction as the heel also having a 12xc3x978, 96 wire construction. The middle bead core has an 11xc3x978 construction with 88 wires.
In the preferred tire of a size 32xc3x9711.5-15, the inside diameter dh equals 15.70 inches, dm equals 15.64 inches, and dt equals 15.54 inches thus satisfying the relationship wherein the middle bead core has a smaller diameter than the heel bead core while the toe bead core dt is greater than or equal to dmxe2x88x92(dhxe2x88x92dm). As in the preferred tire dtxe2x89xa715.60xe2x88x92(15.70xe2x88x9215.60) or dt=15.54 inches which is greater than 15.50.